Electric torque arm helicopter with autorotation safety landing system

ABSTRACT

A battery powered helicopter uses one or more torque arms as the power source directly driving the main rotor blades, causing them to rotate. The helicopter does not require a combustion engine, a clutch, a reducer, a tail driver, a tail boom, a tail rotor, or a fuel supply system. The output shaft of the high-energy motor is coaxial with the main rotor shaft. The centrifugal force of one or more motor(s) is negligible or minimized. The torque arm assembly includes a plurality of torque arms. Each of the torque arms of the plurality of torque arms includes a propeller and a driving system. The torque arm propellers are hinged so that they can move between a first closed position and a second open position to institute an autorotation safety system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of and claims the prioritybenefit of U.S. patent application Ser. No. 16/831,053, filed Mar. 26,2020, now abandoned; which was a continuation-in-part of U.S. patentapplication Ser. No. 16/525,429, filed Jul. 29, 2019, now issued as U.S.Pat. No. 10,604,241, issued Mar. 31, 2020; that application being acontinuation-in-part and claiming the priority benefit of U.S. patentapplication Ser. No. 16/180,004, filed Nov. 4, 2018; which in turnclaims the priority benefit of provisional patent application62/750,462, filed Oct. 25, 2018. These references are incorporated byreference herein in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to helicopters, and moreparticularly to a helicopter using a torque arm assembly as a powersource to drive a main rotor assembly.

BACKGROUND

Currently, the internationally promoted electric helicopters are mostlymulti-rotor structures. It has been developed from the structure ofmulti-rotor drones in recent years. For example, the multi-rotor airtaxis, the jets in the movie Iron Man and the trapeze. Those aircraftsare unlikely to obtain the flight management department's flight permitbecause they (even with installed parachutes) do not meet safe landingrequirement in the event of a failure of the power system. Thosehelicopters are not equipped with autorotation landing functions.

An ideal (desirable flying), electric helicopter is made possiblebecause of high energy motors and highly efficient batteries. Thehelicopter of the present disclosure uses a torque arm assembly withpropellers generating power to drive a main rotor assembly.

A traditional helicopter relies on an engine's output energy to rotate amain rotor assembly. The main rotor assembly generates lifting force sothat the helicopter takes off. A traditional power drive mode is thatthe power of an internal combustion engine, a turboshaft engine or anelectric motor is decelerated by a gearbox. The torque is increased todrive a large-size main rotor assembly.

For a traditional helicopter, while the main rotor assembly is rotating,the entire fuselage also produces a reaction torque with equivalentmagnitude. Therefore, the engine and the fuselage will experience thesame torque as the main rotor assembly. A tail rotor with long tail boomsystem is used to balance this torque. A long tail boom system balancesthe fuselage so that it maintains the direction of the fuselage and thefuselage does not rotate due to the torque of the main rotor assembly.It is conceivable that the transmission system, the balanced torque tailrotor and the long tail boom system not only consume nearly 20% of thepower, but also increase the manufacturing difficulties and controlissues. The increased control issues may cause accidents.

Another traditional way to drive the main rotor assembly is that the jetengine mounted at the tip of the main rotor assembly produces thrustforce to drive the main rotor assembly to rotate. In this way, there isno torque on the fuselage and no longer needs the tail rotor tail boomand a driving system. But it encounters a new issue. When the main rotorassembly is under rotation, the weight of the engine installed at thetip of the rotor generates huge centrifugal force. The jet outputdirection of the jet engine will constantly change following the changeof the blade angle of the rotor blade. The fuel and control transmitthrough the center shaft. The rotary shaft is output to the tip of therotor blade that rotates at a high speed.

Up to now, there are many test models, but there are very few practicalmodels entering the commercial market. An important feature of thepresent disclosure is that the output shaft of the driving motor alignswith an axis of the main rotor shaft so that the centrifugal force ofthe driving motor is negligible (almost zero). A timing belt with acenter distance of approximately 1 meter drives the tip of the propellerfrom inside the torque arm to push or pull the main rotor to rotate. Thetiming belt and the push or pull propellers weigh less than one poundand the centrifugal force is small. The torque is calculated by thethrust force (pulling or pushing the propeller) multiplying the torquearm radius of approximate one meter giving the power torque required forthe main rotor in the unit of kg-meter or N-M. Motor power is deliveredfrom the central shaft to the motor. It increases the drive efficiencyby 35%. If without tail rotor and drive train, the helicopter'smechanical structure has been simplified by 40%. The driving method ofthe present disclosure is especially suitable for light and smallhelicopters. The main rotor of the helicopter is rotated by pushing andpulling of an electric propeller mounted on the tip of the torque arm.Helicopters include torque arm driving system. Applicant's issued U.S.Pat. No. 10,076,763 discloses half-flight and half-walk propeller liftsuspension boom truss module system. A new driving method may be appliedto a helicopter that uses an electric propeller torque arm as the powerto drive the main rotor.

SUMMARY OF THE INVENTION

A helicopter comprises a fuselage, a landing gear assembly, a tailassembly including a directional control rudder assembly, a controlsystem assembly, a main shaft assembly, a main rotor assembly, a motorassembly and a torque arm assembly. The main rotor assembly is rotatableabout a first axis. A centerline of the motor assembly is aligned withthe first axis.

The main rotor of the helicopter requires power to drive it to rotate.The rotating rotor blades cause the air with normal pressure to moverapidly below the rotor. It is generally referred to as “downwashvelocity”, “downwash of the rotor”, or “increased pressure”. Theincreased pressure below the rotor creates an upward lift. The powerabsorbed by a rotor to produce lift is made up of two components:

-   -   1. The power used to increase the momentum of the air in the        vertical direction: Lift HP₁ (first portion of the driving power        for increasing vertical air momentum)        U=√{square root over (L)}/2A _(p)  (1)

where U is the induced vertical velocity of the air in ft/sec,

-   -   L is the lift in lb.    -   A is the swept area of the rotor in ft², and    -   ρ is the density of air.

Therefore, from equation (1), HP1=L×U/550.

-   -   2. The power to rotate the rotor against the drag: The profile        drag HP₂ (second portion of the driving power).

The power to drive the rotation of a helicopter rotor is in two forms:

-   -   A) For a conventional helicopter, the kinetic energy of the        rotary output of an internal combustion engine or a turboshaft        engine and a high-energy motor is transmitted from the main        shaft to the rotor hub through a clutch, a reduction gearbox,        and an overrunning clutch so as to rotate the rotor blades.    -   B) Power from the ramjet mounted on the outer end of the rotor,        an engine, a turbojet, or a hydrogen peroxide jet is injected        from the tip of the rotor to generate thrust to drive the main        rotor blades to rotate.

In order to safely apply the necessary functions of the autorotation inthe event of an engine failure, the helicopter must include a designwith an optimal autorotation rotor system. For helicopters in productiontoday, the high energy rotor systems provide the pilots of thehelicopters with optimal autorotation functions.

Only the French DJINN helicopter meets higher autorotation criteria.Other co-axial power-driven helicopters having two-layer rotors rotatingrelative to each other, having no torque acting on the fuselage, and notintegrating with tail rotor and tail drive systems, experience thecomplexity of the engine transmission system and the rotor hub controlsystem. The reduction of the autorotation drop efficiency is caused bythe aerodynamic interference of the upper and lower rotors and thecoaxial up-and-down counter-rotation rotor. The efficiency is increasedin climbing and hovering. It is in the opposite under the condition ofautorotation landing. Thus, the performance is not as good as asingle-blade traditional helicopter autorotation safe landing.Therefore, for safety reason, it is critical to use a large diametermain rotor having a small disk load per square foot (for example, 1.5lb/ft²) to achieve optimal aerodynamic design. The selection aboveincludes consideration of: trade studies of the main rotor geometrybeing made for solidity, tip speed, diameter, airfoil, chord and twist.In this way, large diameter for freely rotating and small weight arekeys to meet safe autorotation landing requirements.

In one example of a prototype of the present disclosure, the (empty)fuselage structure weighs 254 pounds. The additional second battery packweighs 30 pounds. The pilot weighs 220 pounds. The helicopter grossweight is 504 pounds (230 kg). The helicopter has an 18.5-ft diameterdimension with a 5.6-inch chord rotor, operating at 550 feet per secondtip speed. Each blade weights 11 lbs. of which 1 lb. is distributed atthe tip to produce a high inertia rotor for efficient autorotation. Itresults in a disc loading of 1.5 lb/ft², with a requirement of 32horsepower to hover in a 2,000 ft and 70° F. environment.

The electric propeller will be used to directly drive the main rotor ofthe helicopter through the torque arm assembly. The torque equation is:T _(R) =h,p,×550/2π)×N  (2)

-   -   where T_(R) is the main rotor torque in lbs-ft, and        -   N is rotor speed in revolutions per second.

While the rotor is rotating at 8.3 revolutions per second, the torque is311 lb.-ft (43 kg-m; 420-NM). The calculated results show that a torquearm of approximate one meter in length (0.9 meter to 1.1 meter) issufficient to generate a torque of 43 kg-m for the main rotor assembly.

The driving power is reduced from 32 hp to 16 hp. The efficiency isdoubled. The fly time limit of the electric helicopter will be more thanone hour. It is a manned helicopter with safely autorotation landingcapability. It meets the requirement of FAA FAR Part-103.

The advantages of using an electric propeller torque arm as the power todrive the main rotor include:

1. The driving efficiency is increased by 35% because of direct drivingand without tail rotor system and main drive train.

2. The helicopter's mechanical structure has been simplified by 40%.

3. It is easier to hover especially in a cross-wind condition.

4. It provides static longitudinal stability at all air speeds.

5. The rotor operates at lower angles of attack, that is, the angle atwhich the blade stalls are far removed from the normal flight bladeangle. This allows a wide margin of safety.

6. VTOL (vertical takeoff and landing) operations at high altitudes andhigh temperatures are possible.

7. Rotor speed is not critical because the present disclosure allowsoperation over a wide range of RPM with an overspeed capability as muchas 30% over the recommended RPM.

8. The ability to accelerate forward and climb simultaneously in asmooth and powerful manner is improved.

9. Slower power-off descents using the inertia stored in the main rotorand torque arm for safe autorotation landings are possible.

10. Gyroscopic stabilization due to the massive main rotor plus torquearm is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a helicopter in examples of the present disclosure.

FIG. 2 is an exploded view of a driving assembly including a torque armassembly and a main rotor assembly of a helicopter.

FIG. 3 is a cutaway view of a torque arm assembly showing the drivemechanism.

FIG. 4 is a cutaway view of a torque arm assembly.

FIG. 5 shows the driving mechanism of the torque arm assembly andpropeller.

FIG. 6 illustrates the drive control mechanism and power supplycomponents.

FIG. 7 depicts a torque arm assembly with a droop angle.

FIG. 8 illustrates the hinging mechanism of the torque arm propellerused in the autorotation function.

DETAILED DESCRIPTION

FIG. 1 is a helicopter 100 according to various embodiments of thepresent disclosure. It should be noted that the helicopter may be amanned helicopter, an unmanned helicopter, or a multiple-rotor drone.The helicopter 100 comprises a fuselage 102, a landing gear assembly104, a tail assembly including a directional control rudder 106, acontrol system assembly 108, a main shaft assembly 110, a main rotorblade 112, a motor assembly 114 and a torque arm assembly 116. Inexamples of the present disclosure, the landing gear assembly 104 isdirectly attached to a bottom portion of the fuselage 106. Thedirectional control rudder of the tail assembly 106 is directly attachedto a back portion of the fuselage 102. The control system assembly 108is attached to the fuselage 102. The main shaft assembly 110 is attachedto the control system assembly 108. The main rotor blade 112 is attachedto the main shaft assembly 110. The torque arm assembly 116 is attachedto the main shaft assembly 110. The rotor blade 112 may be positionedbetween the fuselage 102 and the torque arm assembly 116 on the mainrotational axis 118. In various embodiments of the present disclosure,the motor assembly 114 is centered on the main rotational axis 118. Themotor assembly 114 may include multiple motors, each of whose driveshafts has a centerline coaxial with or parallel to the main rotationalaxis 118. Similarly, the torque arm assembly 116 is centered on and iscoaxial with the main rotational axis 118.

In examples of the present disclosure, the rotor blade 112 is rotatableabout the main rotational axis 118. A centerline of the motor assembly114 is aligned with the main rotational axis 118. The motor assembly 114drives the torque arm assembly 116. It will be noted that the torque armassembly is a powered torque arm, but for brevity of expression, thepowered torque arm assembly will be referred to herein as a torque armor torque arm assembly. In embodiments of the present disclosure, thetorque arm assembly 116 may comprise multiple torque arms (see FIG. 4).Each torque arm of the torque assembly 116 comprises a torque armpropeller 122. The torque arm propeller 122 is rotatable about thepropeller axis 120. The propeller axis 120 is perpendicular to the mainrotational axis 118. In examples of the present disclosure, each torquearm of the torque arm assembly 116 is about one meter in length. Thelength of each torque arm of the torque arm assembly 116 is in the rangefrom 0.9 meter to 1.1 meter.

In various embodiments of the present disclosure, a plurality of motorsis included in the motor assembly 114. Each motor drives a correspondingtorque arm propeller 122 through a bevel gear set 406 and a drive shaft410 (see FIG. 4). The propeller is powered by electric power transmittedfrom a center of the main shaft assembly 110. The main rotor blade 112generates push-pull force. Therefore, the rotor blade 112 rotates withan energy in the order of kilogram-meters. The torque arm propeller 122generates torque and pulls a tip of a torque arm of the torque armassembly 116 so that the torque arm assembly 116 rotates eitherclockwise or counterclockwise.

In examples of the present disclosure, the motor assembly 114 is poweredby a battery (shown in FIG. 6). In examples of the present disclosure,the helicopter 100 excludes an engine and excludes a mechanicaltransmission system on the fuselage 102. In examples of the presentdisclosure, the directional control rudder 106 excludes a tail boom andexcludes a tail rotor system balancing torque.

FIG. 2 is an exploded view of a driving assembly 200 of a helicopteraccording to the present disclosure. The driving assembly 200 comprisesthe control system assembly 108, the main shaft assembly 110, the rotorblade 112, at least one motor assembly 114, and at least one torque armassembly 116.

Each torque arm of the plurality of torque arms in the torque armassembly 116 includes a torque arm tube 202 and a torque arm propeller122. The torque arm tube 202 is preferably made of a lightweight,high-strength carbon fiber material. The length (radius) of each torquearm of the torque arm assembly 116 is in a range from 0.9 meter to 1.1meter so as to generate sufficient lifting force without addingsignificant weight. The torque arm propeller 122 is preferably alarge-pitch, high-speed propeller. Each torque arm propeller 122 ismounted on a distal end (tip) of the torque arm.

The main rotor assembly 112 includes a rotor blade 204 and a rotor hub206. The main shaft assembly 110 includes a shaft 208. The motorassembly 114 includes at least one high-energy direct-current (DC) motor210, a motor cover 212 and a motor housing 214. In examples of thepresent disclosure, the high-energy DC motors 210 are mounted coaxiallywith the main shaft assembly 110. A diameter of a bottom portion of themotor cover 212 is approximately equal to the diameter of a top portionof the motor housing 214. As mentioned above, multiple sets of torquearms may be installed on the main rotational axis 118.

A motor speed controller can be installed in the motor housing 214. Themotor housing 214 is preferably made of an aluminum alloy material andthen processed by a computer numerical control (CNC) machining. Inexamples of the present disclosure, the motor housing 214 is formed by awelding process followed by CNC machining.

The control system assembly 108 includes a swashplate system assembly216 and a control system housing 218. The swashplate assembly 216 of thecontrol system assembly 108 includes swashplate control servos,collective pitch control servos and electronic control system.

FIG. 3 is an exploded view of a torque arm assembly 116 mounted on themain rotational axis along with the rotor blade 112 and at least onemotor 210. The motor 210 is encased in a motor housing 302. The torquearm assembly 116 includes a torque arm tube 202 and a timing pulley 304.The timing pulley 304 is a synchronous timing pulley mounted on theoutput shaft of the high-energy motor 210. A timing pulley 304 isrequired for each torque arm propeller 306 utilized in a givenembodiment. Each timing pulley 304 is mounted on an output shaft of themotor 210 which is coaxial with the main rotational axis 118. A timingbelt 308 connects the timing pulley 304 to a torque arm propeller 306.The timing belt 308 is a high-intensity synchronous timing belt. Invarious embodiments, the timing belt 308 has a span distance (centerdistance) of about one meter. The motor 210 drives the torque armpropeller 306 via the timing pulley 304 and the timing belt 308. Therotor blade 112 is mounted coaxially with the motors 210.

FIG. 4 is a cutaway of the torque arm assembly 116. In exemplaryembodiments, the torque arm assembly 116 has four torque arms and acoupling joint 404. Each torque arm of the torque arm assembly 116includes a torque arm tube 202, the coupling joint 404, a motor housing14, a bevel gear set 406, a flexible coupling 408, a plurality ofhigh-energy motors 210, and a drive shaft 410. The bevel gear set 406connects the drive shaft 410 to the torque arm propeller 122. The torquearm propeller 122 is driven by the drive shaft 410 through the bevelgear set 406. The coupling joint 404 may be made of an aluminum alloymaterial. The coupling joint 404 connects the torque arm tube 202 to themotor assembly 114. The motor housing 214 of the central motor assembly114 may be made of an aluminum material and is processed by CNCmachining. The bevel gear set 406 contains right-angle bevel gears. Thedrive shaft 410 may be made of a carbon fiber material. In examples ofthe present disclosure, a first distance between the main rotationalaxis 118 and the respective center of each motor 210 is at least fifteentimes smaller than a second distance between the axis 118 and arespective center of each torque arm propeller 122 of the plurality oftorque arms of the torque arm assembly 116.

FIG. 5 shows the drive assembly 500 of a helicopter in examples of thepresent disclosure. The drive assembly 500 comprises a control systemassembly 108, a main shaft assembly 502, a rotor blade 112, and a torquearm assembly 116. Each torque arm 504 of the torque arm assembly 116 hasa droop angle (illustrated in FIG. 7). Each centerline 506 of acorresponding torque arm 504 of the plurality of torque arms of thetorque arm assembly 116 forms a droop angle with respect to the mainrotational axis 118. The advantage is to reduce the interference of thecomponent force of the torque arm 504 asserted on the rotor blade 112.This lowers the center of gravity of the torque arm assembly 116, thusimproving the stability of the rotation of the rotor blade 112.

The main rotor blade 112 of the helicopter is driven by the powertransmitted via the main shaft assembly 502. The power unit must bedriven by the main shaft so that the fuselage has no reaction torque.The power unit has a weight of at least a few kilograms per horsepower.According to the theoretical formula of centrifugal force:F=W/g×(Angular Velocity in Radians/Sec.)² ×K _(R)(Radius of CG)

-   -   where F is the centrifugal force in lbs.;        -   W is weight in lbs.;        -   g is acceleration due to gravity (32.2 ft/sec/sec); and        -   K_(R) is radius of gyration in ft.

The weight W of a motor with a large horsepower is in the order ofseveral pounds. If the motor is installed in the middle or tip of themain rotor assembly, the radius R will be a dozen feet. From Wmultiplied by R and multiplied by the square of the angular velocity,the value of the centrifugal force will exceed several thousand pounds(in the order of tons).

An important aspect of the present invention is that the motor W isfixed at the center of the rotating shaft so that the radius R is zero(or almost zero). The centrifugal force generated by the very heavymotor is zero (or almost zero). This makes the power system of thepresent disclosure practical for manned light-weight helicopterapplications.

The electric propeller drives the torque arm of the main rotor. Thecentrifugal force of the torque arm system has three portions:

The first is to drive the motor. Since its output shaft is coaxial withthe rotation axis of the main rotor, R is zero, so the centrifugal forceof this portion is zero (or almost zero), and can be neglected.

The second is the torque arm and the weight W of the synchronous timingbelt or driving shaft. Radius R is measured from the center of therotary mass. The torque arm tube is made of carbon fiber composite andmay weigh about 800 grams. The synchronous toothed belt with a centerdistance of one meter has a weight of 112 grams. Radius K_(R) ofgyration is calculated. This is the point where all the weight of asingle rotor blade can be considered to act for the purposes ofcalculating the centrifugal force. The radius of gyration is determinedby considering all the weight is concentrated at the point used tocalculate the centrifugal force. The radius of gyration of a flatsection rotating about one end:K _(R) ² =R ²/3  (4)

The third is the centrifugal force generated by pushing and pulling thepropeller and the small transmission timing pulley or the bevel gear setwith the weight W (About 200 grams) with radius R. On the torque arm,the determination of the position of radius R of the driving propellerdepends on two major factors: Firstly, the rotation speed of theconcentration point is suitable for pushing and pulling the workingrequirements of the propeller, and with suitable speed and pitch of thepropeller. Power is adapted to drive the blade of main rotor and meetsthe requirement of the tip speed. Secondly, if the distance from thecenter of rotation R is too large, the transmission requirements areincreased, the weight is increased, and the centrifugal force isincreased.

The conclusion of the test is that R=1.0 m is a suitable radius. Thetorque is in kg-meter or newton-meter. The rotational speed at thisradius is approximately 200 km/h (50 m/s). It is the suitable workingrange for the push-pull propeller. The top of the main rotor hub of thehelicopter is connected to a coupling joint aligned with the helicoptermain shaft, for driving the rotation of the helicopter main shaft. Themain shaft of the helicopter is a conventional hollow, tubular shaft.The 48V-60V DC power transmission line that drives the DC motor passesthrough the center of the main shaft. The speed control signal of thepower DC motor is transmitted from the center of the main shaft to thetorque arm. The high-energy DC motors 210 may be high-power brushlessmotors having an output shaft aligned with the centerline of the mainrotor of the helicopter.

Referring now to FIG. 6, the power supply assembly 600 includes acontrol module 602 of the motor is mounted in communication with a slipring 606. The control module 602 controls the supply of power from abattery pack 604 to the motor or motors 210. The battery pack 604 istypically located under the pilot's seat.

In order not to cause the driving force of the torque arm mounted on themain rotor hub to be higher than the rotation plane of the main rotor,the torque arm 20 hangs down and has a droop angle alpha as illustratedin FIG. 7. The droop angle allows the center of gravity of the torquearm assembly to be lowered, thereby increasing the stability of therotating rotor blade 112.

In one example of the present disclosure, the helicopter rotor blade 112has a diameter of 18.5 feet. The rotor solidity is reduced to 0.03. Thechord rotor is 5.6 inches. The main rotor hub is a 2-bladed underslungteetering system. The swashplate and the collective pitch control arecontrolled by electronic numerical control servos. It is easier for thepilots of the helicopters to switch to automatic driving systems forautonomous flight and to safely land in an autorotation mode. Thistorque-arm-driven electric single-person helicopter test prototype isproduced in accordance with the requirements of FAA-FAR Part 103. Theempty weight of the helicopter is less than 254 lb. (115 kg). Thefuselage 620 and the landing gears 27 are made of light-weight, carbonfiber or aluminum alloy composite material. The weight of the main rotorassembly 112, the rotor hub 7, swashplate system assembly 9, controlsteering gear and bracket suspension is about 50 pounds. The weight offuselage and the landing gear is 66 pounds. The weight of the drivetorque arm assembly is no more than 22 pounds. LiPo's first battery packis 96 pounds. The remaining accessories are 20 pounds. The sum is 254pounds.

In accordance with FAR Part 103 with 220 pounds limitation for theoccupant or pilot, there is a load of 5 gallons of fuel. It will bereplaced by a second battery pack and weighs 36 pounds. The total weightof the onboard battery of the first and second battery packs is A132-pound (60 kg) lithium polymer battery. Total of 10 KW×h. It willhave a flying time of more than one hour. The total weight of the testhelicopter is 510 pounds (232 kg). The battery pack is under the pilotseat 25. The 48V-60V DC will be transmitted through the hollow spindleto the top torque arm to operate the motor in the center of the torquearm. A synchronous timing belt or driving shaft drives the large-pitchhigh-speed propeller at the outer end of the torque arm to push and pullthe helicopter's main shaft to drive the main rotor to rotate. It issimilar to the “Volga River trackers”.

The torque arm assembly drives the main rotor blade of the helicopter.The larger the radius of the torque arm, the greater the torque and thegreater the centrifugal force. The speed at which the propeller isdriven is increased, and the rotational resistance is also increased. Inone example, the present disclosure uses calculation and manufacturingtechniques to reduce the drag resistance of the torque arm bydetermining an optimal value of the torque arm radius. The helicopter ofthe present disclosure significantly reduces power consumption of thepower-driven mode of the conventional structure of the helicopter byeliminating fuel supply for rotating internal combustion engines orturboshaft engines, by reducing the numbers of gears or belt, and byeliminating the tail rotor. The complexity and weight of the structureis reduced by nearly 40%. It allows the electric helicopter with batterycapacity to increase the flight time by increasing the carrying capacityof the battery pack. At the same time, the driving efficiency of thetorque arm is higher than that of the shaft drive. The increase of thedriving efficiency also allows the battery pack to last longer.Conventionally, it has been tested on small helicopter models to fix themotor directly to the tip of a crossbar (for example, U.S. Pat. No.5,934,873 to Greene), but it is not suitable for larger payload mannedhelicopters because of the huge centrifugal force resulting indifficulty of helicopter control and operation. The present disclosurediscloses that the driving motor is arranged coaxially with the mainrotor so that the centrifugal force of the driving motor is zero (oralmost zero). This driving method can be applied to a manned helicopter.

FIG. 8 shows an assembly according to the present disclosure with animportant safety feature added. The torque arm 116 is driven by a firstbevel gear 81 on the main rotational axis 118 which mates with atranslating bevel gear 82 affixed to the drive shaft 410. Another set ofbevel gears 406 transmits power to the torque arm propeller 122.

The cross-sectional profile of the torque arm 116 is equivalent to thatof an airfoil of an aircraft wing. A suitable choice for the airfoil isthat of NACA 63-3-018. The torque arm 116 has a titanium alloy driveshaft 410, and constitutes a carbon fiber reinforced rigid torque arm116 constructed with a symmetrical airfoil.

If the drive motor 210 stops or the power system fails, an autorotationfunction is initiated so that the pilot can control the helicopter inorder to safely land. In the event the helicopter loses power, the dragof the torque arm 116 needs to be minimized to allow the pilot tocontrol the helicopter. Therefore, each blade of each torque armpropeller 122 includes a hinge 83 that allows the propeller 122 to befolded in order to reduce the rotation resistance. Under normaloperating conditions, as power is applied to the torque arm 116, thetorque arm 116 rotates, and the propeller 122 is moved to the openposition 84 by centrifugal force.

When the autorotation function is initiated due to a loss of power inthe helicopter, the propeller 122 rotates from the open position 84 tothe closed position 85. When power is lost, head-on drag urges thepropeller 122 toward the closed position. The propeller 122 may also bespring loaded, the tension of the spring urging the propeller 122 towardthe closed position 85. With reduced rotation drag, the main rotorblades will speed up, allowing the helicopter to land safely inautorotation mode.

The airfoil section of the torque arm 116 has a good lift-drag ratio.When the pitch angle between the torque arm 116 and the plane ofrotation is 1°, and the helicopter is landing while flying forward at aspeed of approximately 50 knots, the helicopter's and the torque arm'slift-drag vector can be divided into two components, one actingvertically to overcome weight (gravity), and the other actinghorizontally to pull forward on the torque arm.

Those of ordinary skill in the art will recognize that modifications ofthe embodiments disclosed herein are possible. For example, a totalnumber of torque arms may vary. Other modifications may occur to thoseof ordinary skill in this art, and all such modifications are deemed tofall within the purview of the present invention, as defined by theappended claims.

What is claimed is:
 1. A helicopter comprising: a torque arm assemblyrotatable about a main rotational axis, the torque arm assemblycomprising a plurality of torque arms, each of the torque armscomprising a torque arm propeller, a timing pulley, and a timing beltthat connects the timing pulley to the torque arm propeller, such thatthe motor assembly drives the torque arm propellers via the timingpulley and the timing belt; a main rotor blade mounted coaxially withthe torque arm assembly and rotatable about the main rotational axis; amotor assembly mounted coaxially with the torque arm assembly andoutside a fuselage of the helicopter, the torque arm assembly beingrotatable about the main rotational axis; a main shaft assembly; and abattery pack, power from the battery pack being transmitted through aslip ring to the motor assembly via a center channel in the main shaftassembly; wherein the motor assembly drives the torque arm propellers,and torque generated by the torque arm propellers rotates the torque armassembly and the main rotor blade about the main rotational axis; and atleast one of the torque arm propellers is hinged so that it can movebetween a first closed position and a second open position.
 2. Thehelicopter of claim 1, wherein a centerline of each torque arm of thetorque arm assembly is in a plane perpendicular to the main rotationalaxis.
 3. The helicopter of claim 1, wherein the motor assembly comprisesa plurality of motors and wherein a centerline of each of the pluralityof motors is coaxial with the main rotational axis.
 4. The helicopter ofclaim 1 further comprising a control module, the control modulegenerating control signals that are transmitted through the slip ring tothe motor assembly.
 5. The helicopter of claim 1, wherein the helicopteris a manned helicopter, an unmanned helicopter, or a multiple-rotordrone.
 6. An apparatus comprising: a torque arm assembly rotatable abouta main rotational axis, the torque arm assembly comprising a pluralityof torque arms, each of the torque arms comprising a torque armpropeller, a timing pulley, and a timing belt that connects the timingpulley to the torque arm propeller, such that the motor assembly drivesthe torque arm propellers via the timing pulley and the timing belt; amain rotor blade mounted coaxially with the torque arm assembly androtatable about the main rotational axis; a motor assembly mountedcoaxially with the torque arm assembly and outside a fuselage of thehelicopter, the torque arm assembly being rotatable about the mainrotational axis, the motor assembly comprising a plurality of motors, acenterline of a drive shaft of each of the plurality of motors beingparallel to the main rotational axis; a main shaft assembly; and abattery pack, power from the battery pack being transmitted through aslip ring to the motor assembly via a center channel in the main shaftassembly; wherein the motor assembly drives the torque arm propellers,and torque generated by the torque arm propellers rotates the torque armassembly and the main rotor blade about the main rotational axis; and atleast one of the torque arm propellers is hinged so that it can movebetween a first closed position and a second open position.
 7. Theapparatus of claim 6, wherein a centerline of each torque arm of thetorque arm assembly is in a plane perpendicular to the main rotationalaxis.
 8. The apparatus of claim 6, wherein the motor assembly comprisesa plurality of motors and wherein a centerline of each of the pluralityof motors is coaxial with the main rotational axis.
 9. The helicopter ofclaim 6, further comprising a control module, the control modulegenerating control signals that are transmitted through the slip ring tothe motor assembly.